Preparation of viscose sirup



Patented Nov. 29, 1938 UNITED STATES PATENT OFFICE PREPARATION OFVISC'OSE SIRUP George A. Richter, Berlin, N. H., assignor to BrownCompany, Berlin, N. H., a corporation of Maine No Drawing. ApplicationMay 1, 1937, Serial No. 140,222

4 Claims. (01. 260-100) This invention relates to the preparation ofkraft base pulp. The filterability test employed viscose and has for itsgeneral objective the .ecoherein is performed under standard conditionsnomical preparation of viscose sirup such as is with a filter pad ofstandard structure and area; suitable for the manufacture of artificialsilk, and the volume of viscose sirup filtrate delivered 5 films, andregenerated cellulose products. by the pad before it becomes pluggedwith fiber 5 In accordance with the present invention, visfragments orgelatinized particles present in the cose sirup is prepared by theXanthation of alkali r p s taken s the filterebility 0f the pcellulosecomprising a blend of acid-preliberated When viscose sirup was preparedpursuant to the cellulose pulp of the nature of sulphite pulp andinvention hereof from a blend consisting of about alkali-preliberatedcellulose pulp of the nature equal proportions of the same sulphite pulpand 10 of kraft and soda pulps, although krait or simthe same kraft pulpproductive of the viscose ilar alkali-preliberated pulps do not bythemsirups whose filterabilities have just been given, selves yieldvviscose sirups satisfactory for the it was found that the viscose siruphad a filtermanufactureof artificial silk, films, and similar ability ofabout 1400 to 1600, that is, partook in ultimate products, the blendingtherewith of upsurprisingly large measure of the quality of fil- Wardsof about 25% sulphite or similar acidterability possessed by the viscosesirup prepared preliberated pulp, based on the weight of the from thesulphite pulp alone, despite the fact blend, preparatory to Xanthationmakes possible that the sulphite pulp and the kraft base pulp theobtainment of viscose sirups quite satisfachad app ox t y the SameSolution Viscosity tory for manufacture into such ultimate prodasmeasured by the usual cuprammom'um cel- 20 ucts. lulose solution test.

The advantages to be realized from the prac- While it is difficult toaccount for the results tice hereof may perhaps be best appreciated by ed y the practice hereof, y y y considering the results realized whenacid-prelibp ps be explai y What pp s whe Grated Wood pulp, such assulphite, and lkalialkali-cellulose crumbs are prepared fromsulpreliberated wood pulp, such as kraft, separately phite p p alone andfrom kiaft p p aloneundergo the usual Viscose-making 0perati0ns Thus,alkali-cellulose crumbs prepared from sul- These operations involvedipping sheets of the phite pulp are Characterized y a fiuffy p pulp instrong caustic soda solution, pressing the Structure Permitting Teddyand Substantially sheets to form alkali cellulose of appropriate formaccess of Carbon bisulphide Vapor g 30 solution content, grinding tsheets t crumbs out such structure. Per contra, alkali-cellulose orshreds, aging the crumbs, and xanthating the Crumbs Prepared from Kraftp p are of crumbs by tumbling them in a slowly revolving atively dense,Course, and stringy texture drum in the presence of carbon bisulphidevapor. because of non-uniform access of carbon bi- When xanthate crumbsare thus prepared from p e Vapor to their interiors, y d dense, O5sulphite pulp, it is found that they dissolve reado y X n hate r m Wh itanc ow rd ily and substantially completely in dilute caustic sumcientlycomplete dissolution in dilute caustic soda solution to yield acellulose xanthate solu- Soda Solution has already been mentioned. It stion or viscose sirup suitable for the manufacture evidently the casethat n the alkali-cellulose of artificial silk. When, on the other hand,Xanproduct of sulphite p p and the u ose thate crumbs are similarlyprepared from kraft product of Kraft p are ground Simultaneously pulp,it is found that they are resistant to subinto s, the resulting ass orblend of stantially complete dissolution in dilute caustic Crumbs isrendered sufficiently o inous or soda solution and that the resultingviscose distended 50 that h the s iS l to a sirup contains a substantialresidue of fiber low y ro at d a d Xehthated y exposure fragments orgelatim'zed particles bespeaking into carbon bisulphide vapor, the vaporcan pencomplete Xanthation of the pulp and inutility of etrate into andthroughout the distended or volthe viscose sirup for the manufacture ofartificial uminous mass With sufficient rapidity and unisilk. The factis that in terms of filterability or formity to yield Xanthate crumbs ofthe desired capacity for filtration the iscose sirup preparedsubstantially 001111016178 solubility in dilute caustic 50 from sulphitepulp generally displays a filtrasoda solution to conduce to viscosesirup suitable bility of about 1500 to 1800 cubic centimeters as formanufacture into artificial silk. compared with a filterability of onlyabout 100 A typical example of procedure in conformity to 200 cubiccentimeters in the case of viscose with the invention hereof may involvethe use of 55 sirup prepared under similar conditions from a bleachedsulphite pulp and bleached kraft pulp whose compositions, other thanpentosan content, may be substantially similar. Thus, the compositionsof the two bleached pulps may be those appearing in the table below:

Sulphite Kraft Alpha cellulose 88 to 89% 88 to 89% 2 to 4 2 to 4Pentosans 2.5 to 4% 5 to 9% Both the sulphite and kraft pulp may bederived from spruce or other coniferous wood and may be used in the formof drier sheets or pulpboards as ordinarily. Equal portions of suchpulps may be steeped in strong caustic soda solution to form alkalicellulose, as by stacking sheets of the sulphite pulp alternately withsheets of the kraft pulp and submersing the stack in the solution withthe sheets in upstanding position. The stack may thus be put into theusual steeping press wherein the sheets may be thoroughly soaked orsaturated with caustic soda solution of about 18% strength at about 20C. for about 3 hours. Excess soaking solution may be drained from thepress and the stack of soaked sheets then pressed to a solution to pulpratio of about 3 to 1, based on the original weight of the sheets. Thepressed sheets may then be taken from the stack and disintegrated intosoda cellulose crumbs in the usual grinders, wherein the grinding of amass of, say, 200 pounds cellulose content may be effected for a periodof about 3 hours at a temperature of about 20 to 24 C. The resultingsoda-cellulose crumbs, which are of fluffy open structure, may then beaged at about 20 C. for about 70 hours, whereupon they may be chargedinto the usual rotary Xanthating drum into which carbon bisulphide inthe form of vapor may be progressively delivered in the amount of, say,about 35%, based on the dry weight of original cellulose, for a periodof about 3 hours while the mass in the drum is kept at a temperature ofabout 25 C. At the end of such period, the resulting porous mass oforange-colored Xanthate crumbs may be sluiced from the xanthating druminto a dissolving tank wherein the xanthate crumbs may be mixed withdilute caustic soda solution predetermined as to volume and causticityto yield viscose sirup of about 7.5% cellulose content and about 6.5%causticity based on the weight of the sirup. The desired substantiallycomplete dissolution of the xanthate crumbs may be had after mixingintimately with the dilute caustic soda solution at about 15 to 20 C.for about 3 to 4 hours. The resulting viscose sirup is a thick clearliquid practically free from unxanthated or incompletely xanthatedresidues and hence of good filterability. Upon being deaerated, asusual, such viscose sirup is spinnable into artificial silk of strengthand color qualities comparing favorably with artificial silks asheretofore manufactured by the viscose process from sulphite pulp orcotton linters.

It is possible to depart in various respects from the particular examplehereinbefore given. Thus, rather than mixing sheets of the sulphite andkraft pulp while they are being dipped or soaked in the strong causticsoda solution, it is possible to dip or soak sheets consisting of ablend of the two pulps; and it is also possible to dip or soak thesulphite pulp sheets in strong caustic soda solution independently ofthe kraft pulp sheets, provided that the resulting sheets of sodacellulose are ground together at the same time so that crumbs or alkalicellulose produced from the sulphite pulp sheets are substantiallyuniformly blended with the crumbs of alkali cellulose produced from thekraft pulp sheets, thereby providing an alkali-cellulose blend or massof the appropriate fiuffiness or voluminous structure for the xanthatingreaction. When sheets of sulphite pulp and sheets of kraft pulp aredipped or soaked in separate caustic soda'solutions, it is possible tooperate under dipping conditions, i. e., time and temperature of dippingand causticity of dipping solution, different for each of the two typesof sheet and designed to promote the formation of the best kind ofalkali cellulose from each type of sheet. Thus, it may be desirable tofurnish for the kraft pulp sheets a dipping or soaking solution of muchgreater causticity, namely, of much greater than 18% strength, and/or tomaintain such sheets in a solution at lower temperature and/or for alonger period of time than in the case of the sulphite pulp sheets. Inthis latter connection, it should be understood that the stronger thedipping solution, the lower the temperature at which it is used, and thelonger the dipping period, the greater is the reactivity of theresulting soda cellulose in the subsequent xanthating reaction.

The invention hereof affords the important advantage that it makesavailable for satisfactory use in the viscose-rayon process the variousalkali-preliberated wood pulps heretofore found unsuitable forviscose-rayon manufacture, including alkali-preliberated .pulps derivedfrom various resinous or deciduous woods which, although lendingthemselves nicely to low-cost pulping by the soda, kraft, and otheralkaline fiber-liberating processes, do not respond to pulping in acidsulphite or similar acid fiber-liberating liquors. The expressionsalkali-preliberated cellulose pulp or alkali-preliberated wood pulp usedherein are meant to include wood pulps derived from both coniferous anddeciduous woods by kraft, so, or equivalent alkaline pulping liquors andto include such pulps in unbleached, semi-bleached, bleached, unrefined,or refined conditions, as all such pulps may advantageously undergo theprocess hereof. Insofar as concerns unbleached or semi-bleachedalkali-preliberated pulps, it will, of course, be appreciated that theirutility herein extends to the making of artificial silk or otherregenerated cellulose products' wherein the color factor is of noparticular materiality but wherein the factor of strength is ofimportance. So far as concerns the factor of strength, regeneratedcellulose products resulting from the process hereof, when thealkali-cellulose blends contain alkali-cellulose produced fromunbleached or semi-bleached alkali-preliberated cellulose pulps, exhibita strength superior to that of the usual regenerated cellulose products.The utility of the instant invention resides more especially in themaking of viscose sirups of a cellulose content and causticity eachranging from about 6% to 10%, since it is the making of viscose sirup ofsuch composition from alkalipreliberated cellulose pulp that haspresented the problem solved in such a simple and satisfactory way bythe instant invention.

I claim:

1. A process of making viscose, which comprises producing analkali-cellulose blend from acid-sulphite-preliberated cellulose pulpand alkali-preliberated cellulose pulp in approximately equalproportions to not less than about 25% of said first-named pulp relativeto the total cellulose content of said alkali-cellulose, xanthating thealkali-cellulose blend, and dissolving the resulting cellulose xanthateto form viscose.

2. A process of making viscose, which comprises grinding into crumbssheets of alkali-cellulose whose cellulose includes bothacid-sulphitepreliberated cellulose pulp and alkali-preliberatedcellulose pulp in approximately equal proportions to not less than aboutof said firstnamed pulp relative to the total cellulose content of saidalkalicel1ulose, xanthating the crumbs, and dissolving the xanthatedcrumbs to form viscose sirup.

3. A process of making viscose, which comprises grinding into crumbssheets of alkali-cellulose comprising at least two different cellulosecomponents, one of said components being acidsulphite-preliberated woodpulp and the other of said components being alkali-preliberated woodpulp of the nature of kraft and soda pulp in such proportions as toyield a blend of alkalicellulose crumbs whose cellulose content isfurnished to the extent of about 25% to by said first-named pulp,xanthating the blend, and dissolving the resulting cellulose xanthate toform viscose.

4. A process of making viscose, which comprises forming alkali-cellulosefrom sheets of acid-sulphite-preliberated cellulose pulp and from sheetsof alkali-preliberated cellulose pulp, simultaneously grinding intocrumbs the sheets of alkali-cellulose produced from both types of pulpin such proportions as to yield a blend of alkali-cellulose crumbs whosecellulose content is furnished to the extent of about 25% to 50% by saidfirst-named pulp, xanthating the blend of alkali-cellulose crumbs, anddissolving the xanthated crumbs to form viscose sirup.

GEORGE A. RICHTER.

